Polymerization mold



Patented May 15, 1945 Richard D. Freeman, Midland, Mich and Gordon P. Schmelter,-Plainfield, 'N. J., 'assignors to The v Dow Chemical Company, Midland, Mich, a corporation of Michigan No Drawing.

Application November 21, 1942, Serial No. 466,484

3 Claims. (01.18-47) derivative illm has no tendency to stick to the This invention concerns molds suitable for the polymerization of resin-forming liquids.

Thepreparation of molded objects from synthetic resins by introducing a resin-forming liquid into a mold and polymerizing it inplace is a well-lmown procedure. From a practical viewpoint, however, the process has been limited to the production of simple shapes, since it has been' necessary to conduct the polymerization in, metal molds, and these cannot be made in intricate de signs without prohibitive expense. The use of molded resinous object. However, if any of the film should cling to the molded piece, it may be removed by a simple bufling operation, or, more molds formed of relatively 'porous' temporary v molding materials suchjas plaster, which are adapted to the ready fabrication of molds of irregular or complex shapes, has actually been out of the question because of the extreme tendof polymerized resins in molds formed of plaster and like porous materials is readily. and efiectively prevented'by coating the inner surfaces of the'mold prior to polymerization with a film of a water-soluble cellulose derivative insoluble in the resin-forming material. .The film thus applied does not interfere with the polymerization. ,itseli but effectively seals or bridges over the pores of the mold and prevents entry of the polymerizable liquid into these pores, thus in:

l curing formation of a smooth surface on the object and facilitating its removal fron'l the mold. The porous molds towhich the process of the invention is applied may be formed of any of the I temporary molding materials conventionally used in casting metals, such as plaster of Paris, "fine molding sand, bentonite mixtures, and the like;

Cementitious materials such as plaster are ordinarily preferred because of the particularease with-which the molds can be prepared.

In practice, in preparing synthetic resinous ob:-

' 'iects, before each polymerization the inner surfaces'of themold are coated, as by dipping, spraying, etc., with a solution of the water-soluble cellulose derivative in any suitable solvent, preferably water, after which the mold isallowed to dry. The 'polymerizable liquid is then poured into the mold and the mold and contents subjected to polymerizing conditions, in, accordance with known practice. When polymerization is conveniently, by simply washing in water. Among the water-soluble cellulose derivatives which may be used, the water-soluble cellulose ethers, particularly methyl cellulose and the water-soluble salts of cellulose glycolic acid, such as sodium cellulose glycolate and ammonium celluose gycolate, are to be preferred.

The use of water-soluble cellulose derivatives according to the invention is greatly superior to the use of water-soluble natural gums, starch, dextrins, glues, vetc. or to conventional lacquers or shellacs as mold coatings. These latter materials form only discontinuous or weak films on the mold surfaces and are entirely ineffective in eliminating sticking of the molded object.

So far as is known, the use of water-soluble cellulose derivatives as mold coatingsis applicable to the polymerization in porous molds of any resin-forming material which can be polymerized to a. solid product. It is of particular value in the polymerization of styrene and other polymerizable vinyl compounds, such as vinyl chloride, vinyl acetate, esters of acrylic and methacrylic acid, and so-forth. The polymerizable compound is employed in liquid form either as the monomeric material or as a partially polymerized product.

The following example will illustrate the lnvention.

Example 7 plaster mold tone usedfor forming a cast of a human head was coated on the inside with a5 per cent aqueous solution'of methyl celluf ,loseandallowed to dry. The treated mold was 1 fllledwith :a'syrupy solution of partially poly-- merlzedstyrene containing about6O 'per cent polymenand then heated at a temperature of 90 0. forfbdays. At the-end of this time the mold was transferred to an annealing chamber where it was allowed to cool gradually. After complete cooling, the mold was. opened withoutany sticking of the polystyrene to the walls. The casting possessed a perfectly smooth surface and excel lent definition. 1 v I It, is to be understood that the foregoing description is illustrative rather than strictly limltatlve, and that the invention is co-extensivein complete, the solid resinous object is easily removed from the mold; In general, the cellulose scope with the following claims.

We claim: 1. A mold for the preparation of a synthetic 2 aavaau resinous object by the polymerization o! a resiniorming liquid comprising a plaster body having a mold cavity therein, the surfaces of the cavity.

beimz coated with a film of a substance selected from the class consisting of water-soluble metiwl cellulose and water-soluble salts of carboxy methyl cellulose.

2. A mold for the preparation of a synthetic resinous object by the polymerization of a resin- Iorming liquid comprising a plaster body having 10 a mold cavity therein, the surfaces of the cavity being coated with a illm of water-soluble methyl cellulose.

3. A mold for the preparation of a. synthetic resinous object by the polymerization of a, resin- !orming liquid comprising a plaster body having a mold cavity therein, the surfaces 01 the cavity being coated with a film of a. water-soluble salt of carboxy methyl cellulose.

RICHARD D. W. GORDON P. BCHMELTER. 

